THE CONSERVATION OF ENERGY. 409 



wlien the equilibrium is lost and when the subject under observation 

 has passed the point where senilization has gone through several 

 changes, and proceeds rapidly, and can not be checked. 



Life will flow on with normal energy so long as the noble elements, 

 the more highly differentiated cells, are in excess both in processes and 

 activity. The noble elements are those cells which take upon them- 

 selves the preponderating role in accomplishing the function of an 

 organ, in contradistinction to those which play but a secondary part 

 as forming the mechanical support of the organ. Since these can 

 not be replaced in due proportion, function will be interfered with 

 and senescence will begin. Connective tissue now tends to fill all 

 gaps and gradually to invade the tissues, and scleroses will arise, 

 placing obstacles in the way of functional discharge; this constitutes 

 disease. "Inasmuch as the individual is merely an aggregation of 

 special organs adapted to a common existence, the increasing deteriora- 

 tion of these functional activities leads toward gradual deterioration 

 of the individual himself, who will gently fade away out of existence" 

 (Tessier). 



The progress of atrophic changes is not regular, either in the general 

 system or in the special organ. All the elements of the mass do not 

 live to the same age. The constituent elements undergo a perpetual 

 restoration, the older disappearing and being replaced by others which 

 have been long maintained in a state of less differentiation, hence of 

 less specialization. As the completed elements disappear the younger 

 ones are matured, hence the compensation is established between 

 atrophy and repair. This movement of partial renovation in tissues is 

 a picture in little of life, the birth of each element, its functional life, 

 senility and death. The explanation of why irregularity should occur 

 in the nutritive activities in the tissues of each organism, and equally 

 in the whole of some organisms, causing individual and constitutional 

 variations, is not so clear. Chemical processes, presumably similar 

 to the small modifications in the cellular arrangements, and the forces 

 that work, must be recognized. In time we may — indeed we must — 

 know what these dynamic features are; then we shall have reached the 

 first step in controlling these variations from a sound working basis. 

 It is certain that these dynamic modifications can not progress indefi- 

 nitely without producing tangible modifications and alterations in mo- 

 lecular activities; this constitutes disease. Atrophy is an anatomical 

 phase of senility, whose irregular distribution is explained by the 

 inequality of cellular existence, and this is again dependent upon the 

 initial impulse of contraction and upon varying states in the medium, 

 and this by the introduction into the tissues of matters foreign to its 

 normal structure. When this occurs it is degeneration. The study 

 of pathologic changes, by which most of the observations have been 



